The present invention relates to a method of and apparatus for detecting a fuel system leak.
In order to reduce hydrocarbon emissions from fuel systems of vehicles fitted with internal combustion engines, it is known to vent the system through a canister containing charcoal for removing the hydrocarbons before they can be released to the atmosphere. However, should an unacceptable leak occur between the canister and the remainder of the fuel system, fuel vapour can leak to the atmosphere, thus releasing hydrocarbons. Forthcoming legislation requires that any such leak should be no greater than approximately 1 mm.sup.2 and it is necessary to test fuel systems so as to detect an unacceptably large vapour leak from the fuel system. This test should be applied by the vehicle engine management system.
Various proposals have been made for testing fuel systems for unacceptable leaks. Such techniques rely on pressurising or depressurising the fuel system to assess the size of any leak. However, such techniques are performed while the engine is running and the vehicle is moving. Movement of the vehicle causes movement or sloshing of fuel in a fuel tank and this gives rise to problems in accurately assessing the degree of vapour leakage by causing unpredictable variations in pressure.